Bunching of fluxons by Cherenkov radiation in Josephson multilayers

Abstract

A single magnetic fluxon moving at a high velocity in a Josephson multilayer ͑e.g., high-temperature superconductor such as BSCCO͒ can emit electromagnetic waves ͑Cherenkov radiation͒, which leads to the formation of stable dynamic states consisting of several bunched fluxons. We find such bunched states in numerical simulations in the simplest cases of two and three coupled junctions. At a given driving current, several different bunched states are stable and move at velocities that are higher than the corresponding single-fluxon velocity. These and some of the more complex higher-order bunched states and transitions between them are investigated in detail.

Fluxon modes in stacked Josephson junctions: The role of linear modes

“…Thus the relative amplitudes of oscillating parts of the fluxon solution are carried over from the plasma oscillations, but the phase oscillations are antiphase to lock the fluxons. 22 Summarizing the characteristics of the bunched state, the amplitude in layer 2 is about ͱ2 times bigger than the amplitude in layers 1 and 3, and the oscillations in the two layers are antiphase and exponentially decaying with a decay constant k given by kϭ␣v/2(v 2 Ϫc Ϫ 2 ). Finally, the angular frequency of the oscillations is given by ϭ1/ͱv 2 Ϫc Ϫ 2 .…”

Fluxon dynamics in three stacked Josephson junctions

“…1͑b͒ of Ref. 4 the fluxon tail and the induced radiation are mirror symmetric. In the case of slightly different junctions, the cancellation is incomplete and this results in oscillatory tails in both junctions.…”

“…12 The characteristic velocities, corresponding to the three linear modes of the plasma waves, 13,14 are obtained by substituting a periodic-wave-type function j ϭA j e i(kxϪt) into the linear equation obtained by setting ␣ϭ␥ϭ0 and linear- The aim of the present study is to understand the dynamics of the fluxons on three damped and biased junctions, one fluxon in each junction, driven in the high-velocity regime. Quite recently the interaction of fluxons in the case of two and three junctions has been investigated by Goldobin et al, 4,5 where it was numerically shown that several fluxons in one of the junctions may bunch due to Cherenkov emission in the adjacent junctions above the Swihart velocity c Ϫ . A symmetric central finite-difference method of second order for both space and time has been implemented for the numerical simulations.…”

“…4 In the case of two identical junctions a combination of two fluxons results in a nonoscillatory tail because of exact cancellation of antiphase oscillations. As shown in Fig.…”

Terahertz Josephson plasma waves in layered superconductors: spectrum, generation, nonlinear and quantum phenomena

“…The radiation should increase greatly if V exceeds the value of the phase velocity of the waves, which is referred to as Cherenkov-effect [55]. In particular, Cherenkov radiation arises [17,51,[56][57][58][59][60][61][62][63][64][65][66][67] in Josephson junctions if the vortex velocity V exceeds the phase velocity c w (q) of the waves with a definite wave-vector q.…”